The present invention relates to a process for producing a polyolefin using gas phase polymerization in which the gas phase polymerization reaction of α-olefin can be smoothly started without using a seed powder.
Hitherto, it has been considered that in the production of polyolefin with a gas phase polymerization reactor using a fluidized bed, the polymerization reaction cannot be smoothly started unless the polymerization is started after a seed powder is previously filled in the gas phase polymerization reactor and fluidization is started, and then a raw material mixed gas, a catalyst and the like are fed to start the polymerization. Thus, the seed powder has necessarily been used, and hence particle diameter and particle size distribution for uniform dispersion of the fluidizing gas, and operation method and composition of the seed powder for realizing the uniform dispersion state have been investigated (see, for example, Patent Document 1 and Patent Document 2).
However, the seed powder used for formation of the fluidized bed must comprise those components which are the same as or similar to the product polyolefin, taking into consideration the fluidizing conditions and the influence on the quality of the product. Therefore, when many kinds of products are to be produced in the same plant, the polymer in the gas phase polymerization reactor must be wholly discharged for changing over of the kinds of products or for carrying out periodical repairing, and a fresh seed powder must be introduced into the gas phase polymerization reactor when the polymerization is restarted. Therefore, the number of operations and the time required for these operations cause problems. Thus, there has been demanded a method for starting the gas phase polymerization according to which the polymerization can be started more conveniently and smoothly.
[Patent Document 1] JP-A-6-1804 (pages 1-3)
[Patent Document 2] JP-A-2004-189961 (pages 1-3)